Summary: Indications of nonlinear deterministic and finite-dimensional structures in time series
of brain electrical activity: Dependence on recording region and brain state
Ralph G. Andrzejak,1,2,
* Klaus Lehnertz,1,
Florian Mormann,1,2
Christoph Rieke,1,2
Peter David,2
and Christian E. Elger1
1
Department of Epileptology, University of Bonn, Sigmund-Freud-Strasse 25, 53105 Bonn, Germany
2
Institut fu¨r Strahlen- und Kernphysik, University of Bonn, Nußallee 14-16, 53115 Bonn, Germany
Received 14 May 2001; published 20 November 2001
We compare dynamical properties of brain electrical activity from different recording regions and from
different physiological and pathological brain states. Using the nonlinear prediction error and an estimate of an
effective correlation dimension in combination with the method of iterative amplitude adjusted surrogate data,
we analyze sets of electroencephalographic EEG time series: surface EEG recordings from healthy volunteers
with eyes closed and eyes open, and intracranial EEG recordings from epilepsy patients during the seizure free
interval from within and from outside the seizure generating area as well as intracranial EEG recordings of
epileptic seizures. As a preanalysis step an inclusion criterion of weak stationarity was applied. Surface EEG